1. Field of the Invention
The present invention chiefly relates to improvements in a rust-resistant sleeve that prevents rust and corrosion from developing around the wall of a branch hole when the sleeve is rigidly fitted into the branch hole that is drilled through the wall of a metal conduit such as a water pipeline.
2. Description of the Related Art
A rust-resistant sleeve is known and in widely use in water supply systems. Such a rust-resistant sleeve is fitted into a branch hole drilled into the wall of a water pipeline to attain rust and corrosion resistance in the inner surface of the pipeline.
Many of these rust-resistant sleeves are metal sleeves made of copper (phosphor-deoxidized copper), stainless steel or the like, and are directly fitted into a branch hole drilled into the wall of a water pipeline. When the sleeve is installed into the pipeline, undue force works on the sleeve, causing it to be frequently deformed. Such a deformation creates an insufficient contact between the inner wall of the branch hole and the metal sleeve, thereby causing the sleeve to fail to achieve a good rust resistance performance. A technique for increasing rust and corrosion resistance has been developed (Japanese Patent Laid Open Gazette No. 3-96794), in which the outer circumference of the metal sleeve is coated with a water-absorbing swelling rubber.
This technique is intended to fill and seal a void with an expansion of the water-absorbing swelling rubber even if the void takes place in the inner lining of the water pipeline. A sufficient volume of water-absorbing swelling rubber is provided on the lower portion of the metal sleeve. The expansion coefficient of the water-absorbing swelling rubber is generally very large. The water-absorbing swelling rubber expands 20 times larger than its original size in its dry state to the extent that an expanded rubber portion projects out of the sleeve bottom surface. The projecting portion of the rubber may be sometimes torn by a water stream during a long-time service, and may be introduced into the stream of water. A branch pipe is connected to the branch hole, typically with a saddle-type branch stop installed therebetween. A poor connection structure between these components becomes a cause of water leakage and rust. The above-described conventional art offers no steps to assure rust resistance and corrosion resistance.
The portion of the metallic sleeve supporting the flange is made thinner than the remaining portion of the metallic sleeve. When the rust-resistant sleeve is under a longitudinal pressure, the thinner portion first buckles, thereby causing the outer diameter of the flange to increase. Two annular ring portions radially outwardly projecting at both ends of the thinner portion of the metallic sleeve cause the thinner portion to easily buckle.